A device for displaying an abnormal place by turning on an indicator or outputting an electronic sound interlockingly with an indicator in order to warn passengers of occurrence of abnormality such as incomplete door closing or the like is known.
This technique enables passengers of a vehicle to recognize occurrence of abnormality. However, it has a problem that with only an alarm sound the passengers cannot identify a door falling in the incomplete door close state. Furthermore, a warning device for collision avoidance has a problem that with only an alarm sound, passengers cannot immediately specify a site of a vehicle to which another vehicle approaches.
As a countermeasure to the above problem, the applicant of this application has already proposed the technique that virtual sound sources are disposed at warning sites so that passengers can instantaneously identify any abnormal site (warning site) to be warned and hear alarm sounds from the virtual sound sources (JP-A-2003-220911 (page 1, FIG. 14) or US counterpart application US2003/0141967A1).
However, in the above technique, the passengers merely hear alarm sounds from predetermined virtual sound sources, and thus a countermeasure to further enhance the warning effect has been required.
Patent related publications JP-A-2004-251769 and JP-A-5-126948 (U.S. Pat. No. 5,450,057) also disclose techniques for enabling passengers of a vehicle to recognize occurrence of abnormality. However, these publications never disclose a method of generating a virtual sound source, and also leave the acoustic characteristic in the vehicle room out of consideration. Accordingly, it is estimated that it is difficult for these techniques to supply information to a listener from a desired position (make a listener hear a sound).